Frequency-shift carrier distance relay



July 28, 1959 H. w. LENSNER ETAL 2,897,406

FREQUENCSPSHIFT CARRIER DISTANCE RELAY I Filed Sept. 15. 1955 ReuctunceTube Modulator Frequency-Shift Transmitter Output Relay United StatesPatent Office 2,897,405 Patented July 28, 1959 FREQUENCY-SHIFT CARRIERDISTANCE RELAY Herbert W. Lensner, 'East Orange, and George D.Rockefeller, Jr., Morris Plains, N.J., assignors to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania Application September 15, 1955, Serial No, 534,580

Claims. (Cl. 31727) Our invention relates to improvements in protectiverelaying-equipment for the fault-protection of a linesection of acommercial-frequency power-line. It aims at the application offrequency-shift carrier to protective systems in which carrier, or othercommunicatingchannel means, is used in conjunction withdirectionaldistance relays such as have been well established for theprotection of transmission lines. The directional-distance relay-systemoffers a high degree of flexibility in the operation of power systems,and is suited to system-expansion without becoming obsolete. In somesections of the country, carrier for relaying purposes and for otherservices has so saturated the available frequency-spectrum that it hasbecome difiicult to find frequencies for new relaying-channels Whenneeded. In many applications, :also, the attenuation ofcarrier-frequencies is sometimes objectionably, and even prohibitively,high, particularly in applications of carrier relaying to power-cables.

The introduction of frequency-shift carrier to a number of communicationservices such as telemetering'and supervisory control has heretoforeproved to be an ac- :ceptable solution to the problems of limitedchannel-space 'and high attenuation. With crystal-control of thefrequencies, this type of channel requires only a very narrow bandwidthin the frequency-spectrum. It provides improved sensitivity, a lowerresponse to noise and other disturbances, and a smaller bandwidth whichallows expansion of carrier-currentequipment.

of which is a very much'simplified diagram of the essen- =tialconnections, so far as our present invention is concerned.

The drawing illustrates one terminal of aprotected three-phaseline-section L1, which is a part of a 60-cycle transmission-line orpower-system. The protected line- 'section L1 is connected to astation-bus 1 through a threephase line-segregating circuit-breaker CB1,which is illustrated as having two auxiliary make-switches CBla andCBla', and a trip-coil TCI.

The line-section-Ll has'three phase-conductors marked A, B and C. It isprovided with a directional-distance fault-responsive 'means 2, which isillustrated as comprising three panels PA, PB, and PC ofalternating-current connections for phase-fault protection, a fourthpanel PG of alternating-current connections for ground-fault protection,and agroup of relay-contacts which are distinctively marked to designatetheir relation to the alternating-current connection-panels.

The illustrated protective relaying system 2 has four directionallyresponsive elements D, which are distinguished by additional letters.A,B, C, and O for distina guishing between the three line-phases A, B, andC, and the residual or zero-sequence current. This relaying system alsocomprises first-zone phase-fault distance-responsive elements which areillustrated as impedance-elements ZlA, ZlB, and ZlC, for the threephases A, B, and C, and also secondand third-zone phase-faultirnpedance-elements ZZA, ZZB, 22C, and 23A, 23B, and Z3C. It will beunderstood that the third-zone distanceelements are more sensitive thanthe second-zone elements, so as to be able to reach out and respond tofaults in a third protective zone which is more remote from the relayingstation than the second distance-zone to which the second-zone elementsreach. The illustrated relaying system 2 also includes a sensitiveresidual overcurrent relay I08, and a less sensitive residualovercurrent relay IO, the latter having sufficient sensitivity, however,to respond to ground-faults which may lie beyond the remote terminal ofthe protected line-section L1.

The operating coils and the contacts of the various relays aredesignated by the letters which constitute the relay-designation, sothat the relay-designation is sufficient to indicate both theoperating-coils and the contacts of the various elements. The relays areillustrated in their unenergized positions.

The protective relays 2 are energized by line-responsive relayingcurrents and voltages which are provided by means of line-currenttransformers CT, potential transformers PT, auxiliary delta-connectedcurrent-transformers CTl, and auxiliary open-delta potentialtransformers PTI.

In the illustrated protective relaying equipment 2, the third-zonephase-fault distance-elements ZSA, Z3B, and

23C, and the three phase-fault directional elements DA,

DB, and DC, have their current-coils energized from the severalphase-terminals of the star-connected line-current transformers CT,while the firstand second-zone phasefault current-coils 21A to Z2C areenergized from the proper terminals of the auxiliarycurrent-transformers CTl, so as to be responsive to the correspondingdeltacurrents of the protected line-section L1. The threeimpedance-elements of each of the three line-phases havevoltage-restraint windings, which are grouped together under thedesignations ZVA, ZVB and ZVC, respectively, these windings beingenergized from the proper delta phases of the potential transformers PTas indicated. In like manner, the three phase-fault directional elementsDA, DB, and DC have voltage-responsive polarizing coils DVA, DVB, andDVC which are energized from the proper delta phases of the potentialtransformers PT.

The ground-fault relaying panel PG has its three current-coils DO, 10,and T08 energized from the residualcurrent circuit or star-point of theline-current transformers CT. In addition, the directional element DOhas a voltage-responsive polarizing winding DVO, which is excitedresponsively to the zero-sequence line-voltage which is obtained fromthe auxiliary open-delta potential transformers PTL throughvoltage-shifting means which are illustrated in the form of a serieschoke coil X1 and a parallel capacitor C1 which are respectivelyconnected in series and in parallel to the voltage-coil DVO.

In the drawing, a number of direct-current circuits are indicated, afterthe fashion of an across-the-line diagram, from a positive relaying busto a negative relaying bus -A simplified form of the protective relayingcircuits is shown, in which the ground-fault directional-relay contactDO'is connected between the positive bus and a conductor 3, and thencethrough a ground-fault relaycontact IO and a contact 4 of an auxiliaryreceiver-relay RR, to a tripping circuit 5, which is connected to thetripcoil TC1, and thence through the auxiliary breakercontact CBla tothe negative bus The conductor 3 is also used, in a known way, toenergize the operating coil CSG of a ground-fault contactor-switch CSG,the energizing circuit of which is continued on to the negative bus Thethree phase-fault directional-relay contacts DA, DB, and DC are used, ina similar manner, to energize the circuits 6, 7, and 8 respectively,which are connected to the tripping circuit 5 through the first-zonephasefault-relay-contacts Z1A, Z1B, and Z1C respectively. The conductors6, 7 and 8 are also connected to a conductor 9 through three circuitswhich respectively include the second-zone phase-fault relay-contactsZ2A, Z2B, and ZZC, respectively, in a known manner. The conductor 9 isused for two purposes. First, it is connected to the tripping conductor5 through another contact 11 of the auxiliary receiver-relay RR. Theconductor 9 is also used to energize the operating coil CSP of aphase-fault contactor-switch CSP, the energizing circuit of which iscontinued on over to the negative bus The next line 12 of the wiringdiagram shows a receiver-relay operating-coil RR as being connected to aconductor 13 through the make-contact TD of a so-called time-delay relayTD, which is in reality a rather fast relay which operates in some suchtime as one cycle of the power-current frequency, or usually less, so asto serve as a time-hesitation relay for interposing a little bit of timein effecting the closure of the relay-contacts after the energization ofits operating coil TD, as will be subsequently described.

In the drawing, the various electrically operated or controlled relaysand contactor-switches are indicated diagrammatically as havingoperating coils, which are designated by the relay-designation, thesecoils being shown as circles having small concentric circles inside ofthe same, the small inner circles representing armatures or othermovable relay-elements which are lifted in response to an energizationof the operating coils of the respective relays and contactors. Theparticular elementdesignation of each relay or contactor is also appliedto its contact or contacts, as well as to its operating coil, so as todesignate the cooperation between coils and contacts.

The next line 14 of the diagram includes a resistance R1 which isconnected between the positive bus and an intermediate conductor 15,which is continued on, through the back-contacts CSP and CSG of the twocontactors CSP and CSG, and thence to the previously mentioned conductor13.

Next below the circuit 14, in the diagram, come four parallel-connectedcircuits which energize a conductor 16 through any one of the third-zonemake-contacts Z3A, Z3B, or Z3C, or through the sensitive ground-faultmakecontact IOS, respectively. In accordance with our present invention,the circuit 16 is used to energize the operating coil SM of asensitively responsive test-canceling relay SM, which will besubsequently described, this relay being responsive to the actuation ofany one of the four most sensitive fault-responsive elements Z3A, Z3B,Z3C, and IOS. The energizing circuit of the relay-coil SM is continuedon over to the negative bus The intermediate conductor 15, which wasenergized in the line 14 of the circuit-diagram, is also used, in ourinvention, to energize the operating coil TD of the timedelay ortime-hesitation relay TD, through a resistance R2 which is connected tothe circuit 15, so that the TD coil is energized between the circuits 15and 13, thus paralleling the two serially connected back-contacts CSPand CSG.

The circuit 13 is connected over to the negative bus through aresistance R3 which has a value approximately equal to the combinedresistances of the TD coil and the resistance R2. Normally, however, theconductor 13 is also connected to the negative bus through a circuitcomprising the normally closed contact of a testing-pushbutton- PB, acircuit-conductor 17, and the auxiliary breaker-switch CBla' which isclosed when the breaker is closed. Thus, the resistance R3 is normallyshort-circuited, when the line is in operation, and the conductor 13 isconnected directly to the negative bus According to our invention, theconductor 13 is also connected to the negative bus through themakecontact SM of the sensitive test-canceling relay SM, so as to bypassthe testing-pushbutton PB whenever the relay SM is energized by thesensitive fault-detecting elements.

The result of the connections thus far described is that the resistanceR1 is normally connected directly across the positive and negativeterminals and Thus the intermediate conductor 15 is normally at thepotential of the negative bus through a circuit consisting of theback-contacts CSP and CSG, the conductor 13, the test-pushbutton PB, theconductor 17, and the circuitbreaker contact CBla'.

If a ground-fault should occur on the transmission system, accompaniedby a fault-power current-flow into the protected line-section L1 at therelaying station, the auxiliary ground-fault contactor CSG will pick up,opening its back-contact CSG, and increasing the potential of theintermediate circuit-conductor 15 from the potential of the negative buswhich is indicated, for simplicity, as being grounded, to a morepositive potential which is controlled by the relative resistances ofthe resistance R1, the TD coil, and the resistance R2; the circuit 13being still connected to the negative bus This energizes the coil TD ofthe time-delay or timehesitation relay TD, which promptly energizes theoperating coil RR of the auxiliary receiver-relay RR, after the lapse ofa suitable small coordinating time, such as one cycle of the power-linefrequency, for a reason which will be subsequently described.

If a second-zone phase-fault should occur, with an inwardly lookingfault-power direction, the phase-fault contactor-switch CSP picks up,and similarly opens the circuit between the conductors 15 and 13, againshifting the potential of the intermediate conductor 15 from that of thegrounded negative bus to the aforesaid intermediate potential, and againenergizing the time-hesitation relay-coil TD.

According to our invention, the changed potential of the intermediatecircuit 15 is used to modulate a frequency-shift transmitter 18 which islocated at the relaying station. To this end, this intermediateconductor 15 is connected to the negative bus through a largegrid-potential-controlling resistance R4, which is tapped to control thegrid-potential of a reactance-tube modulater 19, which is used tomodulate the frequency of the transmitter 18.

The frequency-shift transmitter 18 preferably has a crystal-controlledoscillator-tube or tubes, and the necesessary butter and amplifier tubes(not shown), for producing a carrier-current output having a narrowradiofrequency f This radio-frequency output is delivered, through anoutput-conductor 21, to a tuner 22, and thence through acoupler-capacitor CC to one of the phase-conductors of the protectedline-section L1. The transmitted carrier energy is largely blocked fromtraveling back to the bus 1, by a suitable line-trap LT. Crystal-tuningis very desirable, because it holds the radio frequencies accurate,between extremely close limits, thus increasing the sharpness of tuning,and narrowing the necessary bandwidth of the radio frequencies.

The transmitter 18 normally transmits its radio-frequency energycontinuously. When our intermediate control-circuit conductor 15 is atthe ground potential of the negative bus the transmitter 18 isoscillating at a so-called mark frequency, which may be any frequency,

or any narrow band of radio freqencies, which is char acteristic of thestate of the transmitter when it is not being modulated by thefault-controlled reactance-tube modulator 19. When a power-line fault,with inwardly looking fault-power direction, shifts the grid-potentialof the reactance-tube modulator 19, the oscillation-frequency isshifted, by the modulator, to a so-called space frequency, which maydiffer from the mark frequency by as little as 120- cycles, more orless, which is an extremely narrow band, in comparison with aradio-frequency which may be anywhere in the range from 40 to 200kilocycles, or the like.

A fault-controlled frequency-shift transmitter 18 is used at eachterminal of the protected line-section L1, except that the narrow bandof transmitted radio-frequency signals is distinctive of the terminalfrom which these signals are being transmitted. Thus, the illustratedline-terminal, having the circuit-breaker CB1, has a distinctivecarrier-current radio-frequency band, which is designated f while thecorresponding transmitter (not shown) at the other terminal of theprotected line-section L1 has a narrow frequency-band which issufiiciently different to be distinguishable, as indicated by thefrequency f which is applied to a radio-frequency receiver 23 at theterminal which is illustrated in the drawing, as will now be described.In other words, each transmitter transmits its distinctive signals tothe remote end or terminal of the protected line-section, and eachterminal-equipment has a receiver 23 which is tuned to receive thesignals which are transmitted from the other terminal of the protectedline-section.

The lower part of the drawing shows a frequencyshift receiver 23,indicated as being responsive to the narrow radio-frequency hand freceiving its radio-frequency input tsrough an input-conductor 24 whichis connected to a separate portion of the tuner 22, and thence to theline, through the coupling-capacitor CC. As shown, the tuner 22 is adouble-frequency tuner, having one circuit 21 which is tuned to thetransmit-ter-frequency or band f at the relaying station, and anothercircuit 24 which is tuned to the receiver-frequency or band 1; at thesame station. The frequency-shift receiver 23 preferably hascrystal-controlled tuning and discriminator circuits, with any necessaryamplifiers, limiters, and relaying-tubes (not shown), discriminativelyresponding to the mark and space frequencies of the transmitter at theother end of the protected line-section L1.

The frequency-shift receiver 23 thus has two outputcirouits, namely amark-response circuit 25 which is energized when the receiversmark-frequency is being received, and a space-response circuit 26, whichis energized when the receivers space-frequency is being received. Thesetwo output-circuits 25 and 26 of the receiver 23 are used to energizethe one or the other of two coils M and S, respectively, of a suitablethreeposition output-relay 27, which has a movable contactmember 28,which is attracted to close a mark contact M when the mark-response coilM is energized, and which is attracted in the other direction, so as toclose a space-contact S when the space-response coil S is energized. Ifneither of the output-relay coils M or S should be energized, themovable relay-contact 23 will return to its normal biased off-position,as illustrated.

According to our invention, the space-response contact S is used tolight a lamp 3%) or other indicating means, for indicating the receiptof the space-frequency signal from the other terminal of the protectedlinesect-ion L1, while the markresponse contact M is used to energizeboth the operating-coil AL of an alarmrelay AL and a holding or blockingcoil RRH of the auxiliary receiver-relay RR, in response to a receipt of.the mark-frequency signal from the other terminal of the protectedline-section.

According to our invention, the alarm-relay AL is provided with aback-contact AL which is used to energize a bell 31 or other indicatingmeans, the ringing of which thus indicates a failure to receive thenormally continuously transmitted mark-frequency signal from the otherteiminal of the protected line-section L1.

The receiver-relay holding-coil RRH is indicated, by means of adownwardly pointing arrow, as a coil which pulls downwardly on theoperating-stem of the auxiliary receiver-relay RR, thus working inopposition to the operating-coil RR which lifts upwardly, as indicatedby its associated arrow. The holding-coil RRH is stronger than theoperating-coil RR, so that the auxiliary receiverrelay RR cannot respondas long as its holding-coil RRH is energized, even though itsoperating-coil RR is simultaneously energized. This is in accordancewith a previously known normal practice in carrier-superviseddirectional-distance relaying-systems.

In the operation of our improved equipment, the frequencysshifttransmitter 18 at each terminal of the protected line-section willnormally be operating continuously at its mark-frequency tuning, with agroundpotential on the control-grid of its reactance-tube modulator 19.Under these circumstances, the bell-circuit at the other terminal willbe held open by the energized condition of the alarm-relay AL, and thelamp-circuit at the other terminal will be deenergized by the nonreceiptof a space-frequency signal.

If a fault should occur on the transmission system, with an inwardlyflowing fault-power direction at the relaying station, one of theauxiliary contactor-switches CSG or C8? will respond, opening itsback-contact between the conductors l5 and 13, thereby shifting thepotential of the reactance-tube grid to a predetermined positive value,which causes the transmitter 18 to shift its output from its markfrequency to its space frequency. At the same time, the opencontactor-switch contact CSG or CSP removes the short-circuit from thetime-hesitation relay TD (if this relay is used), thus causing thisrelay to close and energize the receiverrelay operating-coil RR, at theend of a very brief timehesitation period.

If the fault is an external fault, that is, a fault accompanied by afault-power-flow through the protected linesection and out at the otherend, the energization of the operating-coil RR at the relaying endcannot actuate the receiver-relay RR, because the holding-coil RRHcontinues to be energized by the receipt of the mark-- frequency signalat the relaying station.

If however, the fault is an internal fault, that is, a fault accompaniedby a fault-power-iow into the protected line-section at the remoteterminal, the remote transmitter will have shifted to itsspace-frequency, and the receiver 23 at the illustratedrelaying-terminal will have opened its mark-responsive contact M, thusdeenergizing the holding-coil RRH of the receiver relay RR at therelaying station, permitting this relay to pick up in response to theenergization of its operating coil RR. However, even though theoperating coil RR should become energized before the deenergization ofthe holding-coil RRH, the receiver-relay RR could not.

respond until its holding-coil RRH is deenergized, and

hence the time-hesitation means TD is not needed if the local receiver23 is receiving its mark frequency at the moment when the CSG or CSPcontact opens.

It is a distinctive feature of our invention that we use thecontactor-switch contacts CSG and CSP (or their equivalent) to interruptthe normally continuously transmitted mark-frequency signal at therelaying station, in response to a power-system fault which is accom-.panied by an inwardly flowing fault-current at that station.

In the preferred form of embodiment which is illustrated, we do not useour contactor-switch contacts CSG and CSP to directly remove ashort-circuit from across the operating coil R of the receiver relay, asin previous' carrier-current-directional distance relaying-systems whichhave been in successful use for a number of years, but we use thesecontactor-switch contacts CSG and CSP, or, in general, the relay-ingcircuits 3 and/or 9, to introduce a slight time-hesitation, as by meansof a time-delay relay TD or its equivalent. Our timehesitation relay TDis broadly representative, however, of any means, with or without atime-hesitation, for causing the operating-coil RR of the receiver-relayto be energized (or for causing any equivalent line-protecting functionto be performed), in response to a predetermined fault-indication whichis accompanied by an in-flowing fault-direction at the relaying station.

The provision for a time-hesitation, when used at all (as by means ofour time-delay relay TD), is for the sole purpose of preventing a faultyrelaying-operation in those frequently encountered transmission-systemsin which, in the event of an external fault, that is, a fault on someline-section other than the protected line-section, the opening of thefirst circuit-breaker in the faulted section may sometimes cause asudden reversal of the direction of the throng fault-power flow throughthe protected line-section. In such an event, the fault-power, at oneterminal of the sound protected line-section, will momentarily changefrom an inward direction to an outward direction of power-flow, and thetransmitter at that terminal will quickly change from its spacefrequency to its mar frequency. However, the receiver at the oppositeterminal will require a certain small finite time to close itspreviously open mark-responsive contact M, to thereby energize itsreceiver-relay holding-coil RRH. If it were not for the time-hesitationwhich is provided by the TD relay, the receiver-relay operating-coil RRat this station would have become energized, as soon as thecontactor-contact CSG or CSP opened, and before the energization of itsholding-coil RRH in response to the reversal of the power-flow from aninwardly flowing to an outwardly flowing direction at the oppositeterminal. The time-hesitation thus prevents an erroneoustripping-operation in the sound protected linesection, in the event of asudden reversal of a through fault-current in that line-section when oneof the two circuit-breakers of another, faulted, line-section opens amoment before the opening of the other circuit-breaker of said faultedlinesection.

An important advantage of our application of freequency-shifted carrierto a directional-distance relayingsystem is the ability to thoroughlysupervise the carriercurrent channel, so as to make sure that thecarriercurrent transmitters and receivers are always in a perfectlyoperating condition. The transmitters and receivers are continuouslysupervised by the bell 31 at each terminal of each line-section, becauseas long as the transmitters are operating perfectly, they will betransmitting on their mark frequencies, so that the receivers at theopposite terminals will be holding their mark-contacts M closed, therebyholding their alarm-relays AL energized, and thus holding theirbell-circuits open. The ringing of the bell 31 will thus be an instantindication of a failure of the local receiver to receive its proper markfrequency from the remote transmitter.

While the continuous transmission of the receiver-relayblocking-frequency provides supervision of the carrier-current channelbetween the two terminals of the pro tected line-section, it is alsodesirable to check the ability of the carrier-current equipment to shiftto the spacefrequency and thus to remove the receiver-relay blocking sothat an internal fault may be tripped. The testing circuit to accomplishthis consists primarily of the pushbutton PB in parallel with theresistance R3. An opera tion of the test-pushbutton PB inserts thisresistance R3 in series between the intermediate conductor 15 and thenegative bus thus shifting the potential of the intermediate conductor15 to the same predetermined positive value to which it would have beenshifted by an opening of one of the contactor-switch contacts CSG or CSPin response to an inwardly flowing fault-current. This changes thereactance of the reactance-tube modulator 19 and shifts the frequency ofthe local transmitter 18 from its mar frequency to its space frequencyat the station where the test-pushbutton PE is depressed. At the otherstation or terminal of the protected linesection, the receiver willthereupon respond to this space frequency, causing the closure of itsspace-responsive contact S, and lighting the indicator-lamp at thatstation, thereby demonstrating that the equipment is in a satisfactoryoperative condition.

It will be noted that, during the process of a manual test, thetest-pushbutton PB is being depressed so as to arbitrarily interrupt thenormally continuous transmission of the mar frequency. In most cases, itis required, or at least highly desirable, that if a line-fault shoulddevelop while this manual test is in process, it should still bepossible for the automatic fault-responsive apparatus to properly clearthe fault from the transmission-system. To this end, we use ourpreferably sensitive fault-sensing means, such as the relays Z3A, 23B,23C and 108, such as was heretofore used to start the transmission ofcarrier, in the previously used intermittent carrier system; and we makesensitive fault-sensing circuit energize a test-canceling means, whichhas been illustrated in the form of the SM relay. The effect of thisrelay is to bypass the testing-pushbutton PB, so that thegrid-controlling potential of the intermediate conductor 15 is thereuponbrought back to, and held at, the ground potential of the negative busthus restoring the transmission of the trip-blocking markfrequencysignal, unless and until the directional fault-responsive contact CSG orCSP should open in the normal way, in response to a line-fault which isaccompanied by an inwardly looking fault-power direction.

It will be noted that the second auxiliai'y circuit-breakerswitch-contact CBla', which opens when the local circuit-breaker CB1 isopen for any cause, causes a spacefrequency signal to be sent to theother end of the protected line-section, whenever one end is open, thuspreventing possible improper blocking of an internal endzone fault,

While we have illustrated our invention in a single illustrative form ofembodiment, we wish it to be understood that we are not limited in everyrespect to the precise details shown. For example, while we have shown,and prefer, for reasons well known in the art, the use of a known formof protective relaying means 2 which is responsive to a plurality ofdifferent severities of fault, we are not in every case limited to theresponse to a plurality of different severities. Also, while we haveshown the use of a known form of an auxiliary receiverrelay RR, having astrong hold-coil means RRH and a relatively weaker operating-coil meansRR, and while there are many obvious advantages to this tested and triedform of auxiliary receiver-relay, it would be possible, in the broaderaspects of our invention, to provide, in its place, any kind of meanswhich would perform a fault-protecting function in response to afault-responsive determination of the existence of a predeterminedpower-line fault which has an in-flowing fault-power direction at thatterminal of the protected line-section. Furthermore, the test-cancelingmeans SM may be omitted when its described function may be dispensedwith, in any particular protective equipment. The foregoing and otherchanges of omission or substitution, as well as the addition of manyrefinements, are all to be considered as being within the scope of ourinvention, at least in its broadest aspects.

We claim as our invention:

1. Communicating-channel protective-relaying equipment for thefault-protection of a line-section of a com- 9 mercial-frequ'ency powerline, comprising, at each terminal of the protected line-section, acommunicatingchannel means for transmitting either a normally continuoussignal or an occasional different signal from that terminal to the otherterminal of the protected line-section, both of said signals beingdistinctive of the terminal from which they are transmitted, afault-responsive means for responding to a power-line fault with anin-flowing fault-power direction at that terminal of the protectedline-section, a means for causing said communicatingchannel means tocease transmitting its continuous signal and to start transmitting itsoccasional signal and for also performing a fault-protecting function inresponse to a response of said fault-responsive means, a means forblocking a fault-protecting operation in response to the receipt of thecontinuous signal from said other terminal of the protectedline-section, a test-circuit means for arbitrarily causing saidcommunicating-channel means to cease transmitting its continuous signaland to start transmitting its occasional signal, a test-canceling meansfor incapacitating said test-circuit means in response to a power-linefault, a first indicating means for indicating a failure to receive thecontinuous signal from the other terminal of the protected line-section,and a second indicating means for indicating the receipt of theoccasional signal from said other terminal.

2. Communicating-channel protective-relaying equipment for thefault-protection of a line-section of a commercial-frequency power-line,comprising, at each terminal of the protected line-section, acommunicatingchannel means for transmitting either a normally continuoussignal or an occasional different signal from that terminal to the otherterminal of the protected line-section, both of said signals beingdistinctive of the terminal from which they are transmitted, afault-responsive means for responding to a power-line fault with anin-flowing fault-power direction at that terminal of the protectedline-section, a time-hesitation means which requires a short time torespond, a means for causing said communicating-channel means to ceasetransmitting its continuous signal and to start transmitting itsoccasional signal and for also initiating a response of saidtimehesitation means in response to a response of said faultresponsivemeans, a means for performing a fault-protecting function in response toa completed predetermined response of said time-hesitation means, ameans for blocking a fault-protecting operation in response to thereceipt of the continuous signal from said other terminal of theprotected line-section, a test-circuit means for arbitrarily causingsaid communicating-channel means to cease transmitting its continuoussignal and to start transmitting its occasional signal, a test-cancelingmeans for incapacitating said test-circuit means in response to apower-line fault, a first indicating means for indicating a failure toreceive the continuous signal from the other terminal of the protectedline-section, and a second indicating means for indicating the receiptof the occasional signal from said other terminal.

3. Frequency-shift carrier-current protective-relaying equipment for thefault-protection of a line-section of a commercial-frequency power-line,comprising, at each terminal of the protected line-section, afrequency-shift carrier-current transmitter for transmitting either amark-frequency signal or a slightly different spacefrequency signal overthe protected line-section to the other terminal of said section, bothof said signals having frequencies falling within a narrow band which isdistinctive of the terminal from which they are transmitted, acarrier-current receiver which is tuned to the frequency-bandtransmitted from the other terminal of said protected line-section andwhich is able to discriminate between the mark and space frequencies ofthe transmitter at said other terminal, a fault-responsive means forresponding to a power-line fault with an in-flowing fault-powerdirection at that terminal of the Ylf) protected line-section, a meansfor causing said'transmitter to cease transmitting its mark-frequencysignal and to start transmitting its space-frequency signal and for alsoperforming a fault-protecting function in response to a response of saidfault-responsive means, a means for blocking a fault-protectingoperation in response to the receipt of the mark-frequency signal fromsaid other terminal of the protected line-section, a test- -circuitmeans for arbitrarily causing said communicatingchannel means to ceasetransmitting its mark-frequency signal and to start transmitting itsspace-frequency signal, a test-canceling means for incapacitating saidtest-circuit means in response to a power-line fault, a first indicatingmeans for indicating a failure to receive the mark-frequency signal fromthe other terminal of the protected line-section, and a secondindicating means for indicating the receipt of the spacefrequency signalfrom said other terminal.

4. Frequency-shift carrier-current protectiverelaying equipment for thefault-protection of a line-section of a commercial-frequency power-line,comprising, at each terminal of the protected line-section, afrequency-shift carrier-current transmitter for transmitting either am'ark-frequency signal or a slightly different spacefrequency signalover the protected line-section to the other terminal of said section,both of said signals having frequencies falling within a narrow bandwhich is distinctive of the terminal from which they are transmitted, acarrier-current receiver which is tuned to the frequency-bandtransmitted from the other terminal of said protected line-section andwhich is able to discriminate between the mark and space frequencies ofthe transmitter at said other terminal, a fault-responsive means forresponding to a power-line fault with an in-ilowing fault-powerdirection at that terminal of the protected line-section, a timehesitation means which requires a short time to respond, a means forcausing said transmitter to cease transmitting its mark-frequency signaland to start transmitting its space-frequency signal and for alsoinitiating a response of said time-hesitation means in response to aresponse of said faultresponsive means, a means for performing afault-protecting function in response to a completed predeterminedresponse of said time-hesitation means, a means for blocking afault-protecting operation in response to the receipt of themark-frequency signal from said other terminal of the protectedline-section, a test-circuit means for arbitrarily causing saidcommunicatingchannel means to cease transmitting its mark-fre quencysignal and to start transmitting its -space-frequency signal, atest-canceling means for incapacitating said test-circuit means inresponse to a power-line fault,

a first indicating means for indicating a failure to receive themark-frequency signal from the other terminal of the protectedline-section, and a second indicating means for indicating the receiptof the space-frequency signal from said other terminal.

5. Equipment for providing a communicating channel between two separatedterminals, comprising a communicating-channel means, at each terminal,for transmitting either a normally continuous signal or an occasionaldifferent signal from that terminal to the other terminal, both of saidsignals being distinctive of the terminal from which they aretransmitted, a first intelligence-discerning means, at each terminal,for causing its communicating-channel means to cease transmitting itscontinuous signal and to start transmitting its occasional signal andfor also performing a local function, at its terminal, in response tothat same intelligence, a blocking-means, at each terminal, for blockingthe performance of said local function in response to the receipt of thecontinuous signal from said other terminal, a test-circuit means, ateach terminal, for arbitrarily causing its communicating-channel meansto cease transmitting its continuous signal and to start transmit- 11ting its occasional signal, a second intelligence-discerning means, ateach terminal, for incapacitating the test-circuit means at thatterminal, a first indicating means, at each terminal, for indicating afailure to receive the continuous signal from the other terminal, and asecond indicating means, at each terminal, for indicating the receipt ofthe occasional signal from said other terminal.

6. Equipment for providing a communicating channel between two separatedterminals, comprising, at each terminal, a frequency-shiftcarrier-current transmitter for transmitting either a mark-frequencysignal or a slightly dilferent space-frequency signal to the otherterminal, both of said signals having frequencies falling within anarrow band which is distinctive of the terminal from which they aretransmitted, a carrier-current receiver which is tuned to thefrequency-band transmitted from the other terminal and which is able todiscriminate between the mark and space frequencies of the transmitterat said other terminal, a first intelligencediscerning means for causingsaid transmitter to cease transmitting its mark-frequency signal and tostart transmitting its space-frequency signal and for also performing alocal function, at its terminal, in response to that same intelligence,a blocking-means for blocking the performance of said local function inresponse to the receipt of the mark-frequency signal from said otherterminal, a test-circuit means for arbitrarily causing saidcommunicating-channel means to cease transmitting its mark-frequencysignal and to start transmitting its space-frequency signal, a secondintelligence-discerning means for incapacitating said test-circuitmeans, a first indicating means for indicating a failure to receive themark-frequency signal from the other terminal, and a second indicatingmeans for indicating the receipt of the space-frequency signal from saidother terminal,

7. Equipment for providing a communicating channel between two separatedterminals, comprising, at each terminal, a communicating-channel meansfor transmitting either a normally continuous signal or an occasionaldifferent signal from that terminal to the other terminal, both of saidsignals being distinctive of the terminal from which they aretransmitted, a signaling means for causing said communicating-channelmeans to cease transmitting its continuous signal and to starttransmitting its occasional signal, a receiver-means for responding tothe nonreceipt of the continuous signal from the other terminal, atest-circuit means for arbitrarily causing said communicating-channelmeans to cease transmitting its continuous signal and to starttransmitting its occasional signal, a test-canceling means forincapacitating said testcircuit means in response to an operation of asignaling means at that terminal, a first indicating means forindicating a failure to receive the continuous signal from the otherterminal, and a second indicating means for indicating the receipt ofthe occasional signal from said other terminal.

8. Equipment for providing a communicating channel between two separatedterminals, comprising ,at each terminal, a frequency-shiftcarrier-current transmitter for transmitting either a mark-frequencysignal or a slightly difierent space-frequency signal to the otherterminal, both of said signals having frequencies falling within anarrow band which is distinctive of the terminal from' which they aretransmitted, a carrier-current receiver which is tuned to thefrequency-band transmitted from 12 the other terminal and which is ableto discriminate be tween the mark and space frequencies of thetransmitter at said other terminal, a signaling means for causing saidtransmitter to cease transmitting its markfrequency signal and to starttransmitting its spacefrequency signal, a receiver-means for respondingto the nonreceipt of the mark-frequency signal from said other terminal,a test-circuit means for arbitrarily causing said communicating-channelmeans to cease transmitting its mar -frequency signal and to starttransmitting its space-frequency signal, a test-canceling means for incapacitating said test-circuit means in response to an operation of asignaling means at that terminal, a first indicating means forindicating a failure to receive the n1ark-frequency signal from theother terminal, and a second indicating means for indicating the receiptof the space-frequency signal from said other terminal.

9. Equipment for providing a communicating channel between two separatedterminals, comprising, at each terminal, a communicating-channel meansfor transmitting either a normally continuous signal or an occasionaldifferent signal from that terminal to the other terminal, both of saidsignals being distinctive of the terminal from which they aretransmitted, a signaling means for causing said communicating-channelmeans to cease transmitting its continuous signal and to starttransmitting its occasional signal, a receiver-means for responding toone of the signals from the other terminal, a test-circuit means forarbitrarily causing said communicating-channel means to ceasetransmitting its continuous signal and to start transmitting itsoccasional signal, a first indicating means for indicating a failure toreceive the continuous signal from the other terminal, and a secondindicating means for indicating the receipt of the occasional signalfrom said other terminal.

10. Equipment for providing a communicating channel between twoseparated terminals, comprising, at each terminal, a frequency-shiftcarrier-current transmitter for transmitting either a mark-frequencysignal or a slightly different space-frequency signal to the otherterminal, both of said signals having frequencies falling within anarrow band which is distinctive of the terminal from which they aretransmitted, a carrier-current receiver which is tuned to thefrequency-band transmitted from the other terminal and which is able todiscriminate be tween the mark and space frequencies of the trans mitterat said other terminal, a signaling means for causing said transmitterto cease transmitting its markfrequency signal and to start transmittingits space frequency signal, a receiver-means for responding to one ofthe signals from the other terminal, a test-circuit means forarbitrarily causing said communicating-channel means to ceasetransmitting its mark-frequency signal and to start transmitting itsspace-frequency signal; a first indicating means for indicating afailure to receive the mark-frequency signal from the other terminal,and a second indicating means for indicating the receipt of thespace-frequency signal from said other terminal.

References Cited in the file of this patent UNITED STATES PATENTS2,454,163 Harder Nov. 16, 1948 2,611,041 Cooper Sept. 16, 1952 2,615,985Moynihan Oct. 28, 1952 2,677,014 Moynihan Apr. 27, 1954

